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Annu. Rev. Entomol. 2006.51:45-66. Downloaded from arjournals.annualreviews.org 

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Annu. Rev. Entomol. 2006. 51:45–66 

doi: 10.1146/annurev.ento.51.110104.151146 

Copyright c○ 2006 by Annual Reviews. All rights reserved 

First published online as a Review in Advance on July 11, 2005 

BOTANICAL INSECTICIDES, DETERRENTS, AND 

REPELLENTS IN MODERN AGRICULTURE AND 

AN INCREASINGLY REGULATED WORLD 

Murray B. Isman 

Faculty of Land and Food Systems, University of British Columbia, 

Vancouver, British Columbia, V6T 1Z4, Canada; email: murray.isman@ubc.ca 

Key Words pyrethrum, neem, essential oils, antifeedants, commercialization 

■ Abstract Botanical insecticides have long been touted as attractive alternatives 

to synthetic chemical insecticides for pest management because botanicals reputedly 

pose little threat to the environment or to human health. The body of scientific literature 

documenting bioactivity of plant derivatives to arthropod pests continues to expand, 

yet only a handful of botanicals are currently used in agriculture in the industrialized 

world, and there are few prospects for commercial development of new botanical products. 

Pyrethrum and neem are well established commercially, pesticides based on plant 

essential oils have recently entered the marketplace, and the use of rotenone appears 

to be waning. A number of plant substances have been considered for use as insect 

antifeedants or repellents, but apart from some natural mosquito repellents, little commercial 

success has ensued for plant substances that modify arthropod behavior. Several 

factors appear to limit the success of botanicals, most notably regulatory barriers and 

the availability of competing products (newer synthetics, fermentation products, microbials) 

that are cost-effective and relatively safe compared with their predecessors. In 

the context of agricultural pest management, botanical insecticides are best suited for 

use in organic food production in industrialized countries but can play a much greater 

role in the production and postharvest protection of food in developing countries. 

INTRODUCTION 

The practice of using plant derivatives, or botanical insecticides as we now know 

them, in agriculture dates back at least two millennia in ancient China, Egypt, 

Greece, and India (86, 89). Even in Europe and North America, the documented 

use of botanicals extends back more than 150 years, dramatically predating discoveries 

of the major classes of synthetic chemical insecticides (e.g., organochlorines, 

organophosphates, carbamates, and pyrethroids) in the mid-1930s to 1950s. What 

is clear from recent history is that synthetic insecticides effectively relegated botanicals 

from an important role in agriculture to an essentially trivial position in the 

marketplace among crop protectants. However, history also shows that overzealous 

0066-4170/06/0107-0045$20.00 45



46 ISMAN 

use of synthetic insecticides led to numerous problems unforeseen at the time of 

their introduction: acute and chronic poisoning of applicators, farmworkers, and 

even consumers; destruction of fish, birds, and other wildlife; disruption of natural 

biological control and pollination; extensive groundwater contamination, potentially 

threatening human and environmental health; and the evolution of resistance 

to pesticides in pest populations (35, 63, 70, 72). 

Governments responded to these problems with regulatory action, banning or 

severely restricting the most damaging products and creating policies to replace 

chemicals of concern with those demonstrated to pose fewer or lesser risks to human 

health and the environment. In the United States, these policies are reflected by 

the definition of “reduced risk” pesticides by the Environmental Protection Agency 

in the early 1990s with their favored regulatory status, and by the Food Quality 

Protection Act (1996), which, in reappraising safe levels of pesticide residues in 

foods, is having the net effect of removing most synthetic insecticides developed 

before 1980 from use in agriculture. These changes in the regulatory “environment” 

appeared to heighten the impetus for the discovery and development of alternative 

pest management products—those with reduced health and environmental 

impacts—including insecticides derived from plants. Indeed, the scientific literature 

of the past 25 years describes hundreds of isolated plant secondary metabolites 

that show feeding deterrent or toxic effects to insects in laboratory bioassays, and 

botanical insecticides have been the subject of several recent volumes (28, 40, 57, 

76, 79). 

Yetinspite of the scale of this research enterprise, only a handful of botanical 

insecticides are in commercial use on vegetable and fruit crops today, with significant 

commercial development of only two new sources of botanicals in the past 

20 years. In this chapter I review current botanicals and their trends in use, discuss 

the few botanical materials with potential for future commercialization, suggest 

why so few botanicals reach the marketplace, and finally suggest in what contexts 

botanicals could prove effective in the years to come. 

CURRENT BOTANICALS IN USE 

At present there are four major types of botanical products used for insect control 

(pyrethrum, rotenone, neem, and essential oils), along with three others in limited 

use (ryania, nicotine, and sabadilla). Additional plant extracts and oils (e.g., garlic 

oil, Capsicum oleoresin) see limited (low volume) regional use in various countries, 

but these are not considered here. In discussing the extent to which each of the more 

important botanical insecticides is used, I often refer to data published annually 

by the State of California’s Department of Pesticide Regulation (18). Although 

not necessarily representative of uses in other jurisdictions, total pesticide use (in 

terms of active ingredient applied) in California totaled more than 175 million 

pounds, or 80,000 tonnes, in 2003. This amount represents approximately 6% of 

global pesticide use, of which 91% was used for agriculture. Pesticide use data



BOTANICAL INSECTICIDES 47 

in California are reported by active ingredient and by crop or other use and as 

such are perhaps the world’s most accurate and detailed records of pesticide use 

available to the general public. 

Pyrethrum 

Pyrethrum refers to the oleoresin extracted from the dried flowers of the pyrethrum 

daisy, Tanacetum cinerariaefolium (Asteraceae). The flowers are ground to a powder 

and then extracted with hexane or a similar nonpolar solvent; removal of the 

solvent yields an orange-colored liquid that contains the active principles (21, 

37). These are three esters of chrysanthemic acid and three esters of pyrethric 

acid. Among the six esters, those incorporating the alcohol pyrethrolone, namely 

pyrethrins I (Figure 1) and II, are the most abundant and account for most of 

the insecticidal activity. Technical grade pyrethrum, the resin used in formulating 

commercial insecticides, typically contains from 20% to 25% pyrethrins (21). 

The insecticidal action of the pyrethrins is characterized by a rapid knockdown 

effect, particularly in flying insects, and hyperactivity and convulsions in most 

insects. These symptoms are a result of the neurotoxic action of the pyrethrins, 

which block voltage-gated sodium channels in nerve axons. As such, the mechanism 

of action of pyrethrins is qualitatively similar to that of DDT and many 

synthetic organochlorine insecticides. In purity, pyrethrins are moderately toxic to 

mammals (rat oral acute LD50 values range from 350 to 500 mg kg −1 ), but technical 

grade pyrethrum is considerably less toxic (∼1500 mg kg −1 ) (21). Pyrethrins 

are especially labile in the presence of the UV component of sunlight, a fact that 

has greatly limited their use outdoors. A recent study indicated that the half-lives 

of pyrethrins on field-grown tomato and bell pepper fruits were 2 hours or less (3). 

This problem created the impetus for the development of synthetic derivatives 

(“pyrethroids”) that are more stable in sunlight. The modern pyrethroids, developed 

in the 1970s and 1980s, have been highly successful and represent one of the 

rare examples of synthetic pesticide chemistry based on a natural product model. 

However, note that the modern pyrethroids bear little structural resemblance to 

the natural pyrethrins, and their molecular mechanism of action differs as well. 

Pyrethrum use data from California (18) in 2003 clearly demonstrate the dominance 

of this material among botanicals: Pyrethrum accounted for 74% of all 

botanicals used that year, but only 27% of that amount was used in agriculture 

(∼800 kg). Major uses of pyrethrum in California are for structural pest control, in 

public health, and for treatment of animal premises. Pyrethrum is the predominant 

botanical in use, perhaps accounting for 80% of the global botanical insecticide 

market (49). 

For many years world production of pyrethrum was led by Kenya, with lesser 

quantities produced in Tanzania and Ecuador. In the past five years, Botanical 

Resources Australia, with plantings in Tasmania, has become the second largest 

producer in the world (∼30% of world production at present). Pyrethrum produced 

in Tasmania is qualitatively similar to that produced in East Africa and elsewhere,



48 ISMAN 

Neem 

but the market share achieved by the Australian producer may not increase owing 

to World Bank grants and government subsidies to producers in Kenya and China 

(B. Chung, personal communication). 

Two types of botanical insecticides can be obtained from seeds of the Indian neem 

tree, Azadirachta indica (Meliaceae) (81). Neem oil, obtained by cold-pressing 

seeds, can be effective against soft-bodied insects and mites but is also useful 

in the management of phytopathogens. Apart from the physical effects of neem 

oil on pests and fungi, disulfides in the oil likely contribute to the bioactivity of 

this material. More highly valued than neem oil are medium-polarity extracts of 

the seed residue after removal of the oil, as these extracts contain the complex 

triterpene azadirachtin (Figure 2). Neem seeds actually contain more than a dozen 

azadirachtin analogs, but the major form is azadirachtin and the remaining minor 

analogs likely contribute little to overall efficacy of the extract. Seed extracts 

include considerable quantities of other triterpenoids, notably salannin, nimbin, 

and derivatives thereof. The role of these other natural substances has been controversial, 

but most evidence points to azadirachtin as the most important active 

principle (50). Neem seeds typically contain 0.2% to 0.6% azadirachtin by weight, 

so solvent partitions or other chemical processes are required to concentrate this 

active ingredient to the level of 10% to 50% seen in the technical grade material 

used to produce commercial products. 

Azadirachtin has two profound effects on insects. At the physiological level, 

azadirachtin blocks the synthesis and release of molting hormones (ecdysteroids) 

from the prothoracic gland, leading to incomplete ecdysis in immature insects. In 

adult female insects, a similar mechanism of action leads to sterility. In addition, 

azadirachtin is a potent antifeedant to many insects. The discovery of neem by 

western science is attributed to Heinrich Schmutterer, who observed that swarming 

desert locusts in Sudan defoliated almost all local flora except for some introduced 

neem trees (69). Indeed, azadirachtin was first isolated based on its exceptional 

antifeedant activity in the desert locust, and this substance remains the most potent 

locust antifeedant discovered to date. Unlike pyrethrins, azadirachtin has defied 

total synthesis to this point. Promoted in the United States by Robert Larson (with 

assistance from the U.S. Department of Agriculture), neem rapidly became the 

modern paradigm for development of botanical insecticides. 

Enthusiasm for neem was fostered by several international conferences in the 

1980s and 1990s, and several volumes dedicated to neem and neem insecticides 

have been published (51, 69, 81). Unfortunately, neem’s commercial success has 

fallen well short of the initial hype fueled by the explosive scientific literature surrounding 

it. In part this is due to the relatively high cost of the refined product (48) 

and the relatively slow action on pest insects. Nonetheless, several azadirachtinbased 

insecticides are sold in the United States and at least two such products 

in the European Union. In California, azadirachtin-based insecticides constituted




about one third of the botanicals used in agriculture in 2003 (∼600 kg). In practice, 

reliable efficacy is linked to the physiological action of azadirachtin as an insect 

growth regulator; the antifeedant effect, which is spectacular in the desert locust, 

is highly variable among pest species, and even those species initially deterred are 

often capable of rapid desensitization to azadirachtin (13). 

What is clear is that azadirachtin is considered nontoxic to mammals (rat oral 

acute LD50 is >5000 mg kg −1 ), fish (88), and pollinators (71). The influence of 

azadirachtin on natural enemies is highly variable (62, 83). Like the pyrethrins, 

azadirachtin is rapidly degraded by sunlight. For example, on olives growing in 

Italy, azadirachtin has a half-life of approximately 20 h (16). On the other hand, 

azadirachtin has systemic action in certain crop plants, greatly enhancing its efficacy 

and field persistence (81). 

Plant Essential Oils 

Steam distillation of aromatic plants yields essential oils, long used as fragrances 

and flavorings in the perfume and food industries, respectively, and more recently 

for aromatherapy and as herbal medicines (14, 26). Plant essential oils are produced 

commercially from several botanical sources, many of which are members of the 

mint family (Lamiaceae). The oils are generally composed of complex mixtures 

of monoterpenes, biogenetically related phenols, and sesquiterpenes. Examples 

include 1,8-cineole, the major constituent of oils from rosemary (Rosmarinus 

officinale) and eucalyptus (Eucalyptus globus); eugenol from clove oil (Syzygium 

aromaticum); thymol from garden thyme (Thymus vulgaris); and menthol from 

various species of mint (Mentha species) (45) (Figure 2). A number of the source 

plants have been traditionally used for protection of stored commodities, especially 

in the Mediterranean region and in southern Asia, but interest in the oils was 

renewed with emerging demonstration of their fumigant and contact insecticidal 

activities to a wide range of pests in the 1990s (46). The rapid action against 

some pests is indicative of a neurotoxic mode of action, and there is evidence for 

interference with the neuromodulator octopamine (29, 56) by some oils and with 

GABA-gated chloride channels by others (77). 

Some of the purified terpenoid constituents of essential oils are moderately 

toxic to mammals, but, with few exceptions, the oils themselves or products based 

on oils are mostly nontoxic to mammals, birds, and fish (46, 84). However, as 

broad-spectrum insecticides, both pollinators and natural enemies are vulnerable 

to poisoning by products based on essential oils. Owing to their volatility, essential 

oils have limited persistence under field conditions; therefore, although natural 

enemies are susceptible via direct contact, predators and parasitoids reinvading 

a treated crop one or more days after treatment are unlikely to be poisoned by 

residue contact as often occurs with conventional insecticides. 

In the United States, commercial development of insecticides based on plant 

essential oils has been greatly facilitated by exemption from registration for certain 

oils commonly used in processed foods and beverages (78). This opportunity



50 ISMAN 

Figure 1 Active constituents of some botanical insecticides from various plant sources 

discussed in this review. (a) Nicotine, (b) pyrethrin I, (c) rotenone, (d )cevadine, (e) ryanodine, 

and ( f ) asimicin.




Figure 2 Active constituents of some botanical insecticides from neem (a), Melia species 

(b–d ), and selected plant essential oils (e–k). (a) Azadirachtin, (b) toosendanin, (c) 1cinnamoyl-3-feruoyl-11-hydroxymeliacarpin, 

(d )volkensin, (e) d-limonene, ( f ) menthol, 

(g) 1,8-cineole, (h) citronellal, (i) eugenol, ( j) p-menthane-3,8-diol, and (k) thymol.



52 ISMAN 

has spurred the development of essential oil-based insecticides, fungicides, and 

herbicides for agricultural and industrial applications and for the consumer market, 

using rosemary oil, clove oil, and thyme oil as active ingredients. Interest in these 

products has been considerable, particularly for control of greenhouse pests and 

diseases and for control of domestic and veterinary pests, with several private 

companies (e.g., EcoSMART Technologies, Inc., United States) moving toward or 

into the marketplace. Another factor favoring development of botanical insecticides 

based on plant essential oils is the relatively low cost of the active ingredients, a 

result of their extensive worldwide use as fragrances and flavorings. In contrast, 

pyrethrum and neem are used primarily for insecticide production (R. Georgis, 

personal communication). 

Rotenone and Other Extant Botanicals 

As an insecticide, rotenone has been in use for more than 150 years, but its use as a 

fish poison dates back even further (82). Rotenone is one of several isoflavonoids 

produced in the roots or rhizomes of the tropical legumes Derris, Lonchocarpus, 

and Tephrosia. Most rotenone used at present comes from Lonchocarpus grown in 

Venezuela and Peru and is often called cubé root. Extraction of the root with organic 

solvents yields resins containing as much as 45% total rotenoids; studies indicate 

that the major constituents are rotenone (44%) (Figure 1) and deguelin (22%) (15, 

30). Rotenone is commonly sold as a dust containing 1% to 5% active ingredients 

for home and garden use, but liquid formulations used in organic agriculture can 

contain as much as 8% rotenone and 15% total rotenoids. 

Rotenone is a mitochondrial poison, which blocks the electron transport chain 

and prevents energy production (41). As an insecticide it is considered a stomach 

poison because it must be ingested to be effective. Pure rotenone is comparable 

to DDT and other synthetic insecticides in terms of its acute toxicity to mammals 

(rat oral LD50 is 132 mg kg −1 ), although it is much less toxic at the levels seen 

in formulated products. Safety of rotenone has recently been called into question 

because of (a) controversial reports that acute exposure in rats produces brain 

lesions consistent with those observed in humans and animals with Parkinson’s 

disease (10), and (b) the persistence of rotenone on food crops after treatment. A 

study of rotenone residues on olives conducted in Italy determined that the halflife 

of rotenone is 4 days, and at harvest residue levels were above the tolerance 

limit (17). Moreover, residues were concentrated in oil obtained from the olives. 

As an agricultural insecticide, use of rotenone is limited to organic food production. 

In California, about 200 kg are used annually, mostly on lettuce and tomato 

crops. 

Sabadilla is a botanical insecticide obtained from the seeds of the South American 

lily Schoenocaulon officinale.Inpurity, the active principles, cevadine-type alkaloids 

(Figure 1), are extremely toxic to mammals (rat oral LD50 is ∼13 mg kg −1 ), 

but commercial preparations typically contain less than 1% active ingredient, providing 

a margin of safety. The mode of action of these alkaloids is remarkably




similar to that of the pyrethrins, despite their lack of structural similarity. Sabadilla 

is used primarily by organic growers; in California about 100 kg is used annually, 

primarily on citrus crops and avocado. Another botanical in declining use is ryania, 

obtained by grinding the wood of the Caribbean shrub Ryania speciosa (Flacourtiaceae). 

The powdered wood contains



54 ISMAN 

as insecticides. In spite of the patents based on the insecticidal activities of these 

materials, no commercial development has proceeded with the exception of a head 

lice shampoo that contains a standardized pawpaw extract among its active ingredients 

(Nature’s Sunshine Products, Inc., United States). Annona seed extracts may 

prove more useful in tropical countries where the fruits are commonly consumed 

or used to produce fruit juice, in which case the seeds are a waste product. For 

example, Leatemia & Isman (59, 60) recently demonstrated that crude ethanolic 

extracts or even aqueous extracts of seeds from A. squamosa collected at several 

sites in eastern Indonesia are effective against the diamondback moth (Plutella 

xylostella). 

Sucrose Esters 

In the early 1990s scientists at the U.S. Department of Agriculture discovered that 

sugar esters naturally occurring in the foliage of wild tobacco (Nicotiana gossei) 

were insecticidal to certain soft-bodied insects and mites. Although patented (75), 

extraction of these substances on a commercial scale from plant biomass proved 

impractical, leading to the development of sucrose esters manufactured from sugar 

and fatty acids obtained from vegetable oils. AVA Chemical Ventures (United 

States) has patented and registered an insecticide/miticide based on C8 and C10 fatty 

acid mono-, di-, and triesters of sucrose octanoate and sucrose dioctanoate (31). 

The product, first registered in 2002, contains 40% active ingredient. Functionally, 

this product appears to differ little from the insecticidal soaps based on fatty 

acid salts developed in the 1980s, particularly potassium oleate. Both products 

are contact insecticides that kill small insects and mites through suffocation (by 

blocking the spiracles) or disruption of cuticular waxes and membranes in the 

integument, leading to desiccation. Although useful in home and garden products 

and in greenhouse production, the utility of these materials for agriculture remains 

to be seen. 

Melia Extracts 

The remarkable bioactivity of azadirachtin from the Indian neem tree (Azadirachta 

indica) led to the search for natural insecticides in the most closely related genus, 

Melia. Seeds from the chinaberry tree, M. azedarach, contain a number of triterpenoids, 

the meliacarpins (Figure 2), that are similar but not identical to the 

azadirachtins, and these too have insect growth regulating bioactivities (58). But in 

spite of the abundance of chinaberry trees in Asia and other tropical and subtropical 

areas to which they were introduced, development of commercial insecticides 

has not paralleled that of the neem insecticides. The main reason is the presence, 

in chinaberry seeds, of additional triterpenoids, the meliatoxins, that have 

demonstrated toxicity to mammals (4). However the chemistry of chinaberry varies 

considerably across its natural and introduced range, and seeds of M. azedarach 

growing in Argentina lack meliatoxins but produce triterpenoids (most notably




meliartenin) that are strong feeding deterrents to pest insects and could prove 

useful for pest management (19). Similar results have been obtained from South 

Africa using aqueous extracts of chinaberry leaves, presumably lacking meliatoxins 

but efficacious against the diamondback moth (22). 

In the early 1990s a botanical insecticide produced in China was based on an 

extract of bark of Melia toosendan, atree considered by most taxonomists to be 

synonymous with M. azedarach. The extract contains a number of triterpenoids 

based on toosendanin (Figure 2), a substance reported to be a stomach poison for 

chewing insects (24). Later studies suggest that this substance acts primarily as a 

feeding deterrent but can also serve as a synergist for conventional insecticides (23, 

32). Although relatively nontoxic to mammals, it is unclear whether this material 

remains in production or whether it is sufficiently efficacious as a stand-alone crop 

protectant. 

When M. toosendan came under scientific scrutiny, investigation of the east 

African M. volkensii demonstrated bioactivity in insects from seed extracts of this 

species. The active principles in M. volkensii include the triterpenoid salannin, also 

a major constituent of neem seed extracts, and some novel triterpenoids such as 

volkensin (Figure 2). Collectively these function as feeding deterrents and stomach 

poisons with moderate efficacy against chewing insects and as a mosquito 

larvicide. Although a standardized seed extract has been made in quantities sufficient 

for research (80), commercial production appears unlikely owing to a lack 

of infrastructure for harvesting seeds in addition to regulatory impediments. 

INSECT ANTIFEEDANTS AND REPELLENTS 

Antifeedants 

The possibility of using nontoxic deterrents and repellents as crop protectants is 

intuitively attractive. The concept of using insect antifeedants (=feeding deterrents) 

gained strength in the 1970s and 1980s with the demonstration of the potent 

feeding deterrent effect of azadirachtin and neem seed extracts to a large number of 

pest species. Indeed, considerable literature, scientific and otherwise, touts neem 

as a successful demonstration of the antifeedant concept. In reality, it is the physiological 

actions of azadirachtin that appear most reliably linked to field efficacy 

of neem insecticides (42); although purely behavioral effects cannot be ruled out, 

there is hardly any irrefutable evidence or documentation of field efficacy based 

on the antifeedant effects of neem alone. 

As an academic exercise, the discovery and demonstration of plant natural products 

as insect antifeedants has been unquestionably successful. In addition to the 

neem triterpenoids, extensive work has been performed on clerodane diterpenes 

from the Lamiaceae (55) and sesquiterpene lactones from the Asteraceae (38). 

On the other hand, not a single crop protection product based unequivocally on 

feeding or oviposition deterrence has been commercialized. Two main problems



56 ISMAN 

face the use of antifeedants in agriculture (47). The first is interspecific variation 

in response—even closely related species can differ dramatically in behavioral 

responses to a substance—limiting the range of pests affected by a particular antifeedant 

(43). Some substances that deter feeding by one pest can even serve as 

attractants or stimulants for other pests. The second is the behavioral plasticity in 

insects—pests can rapidly habituate to feeding deterrents, rendering them ineffective 

in a matter of hours. This has been recently demonstrated not only for pure 

substances like azadirachtin (13), but also for complex mixtures (plant extracts) 

(1). Whereas a highly mobile (flying) insect may leave a plant upon first encountering 

an antifeedant, a less mobile one (larva) may remain on the plant long enough 

for the deterrent response to wane. Such behavioral changes are important in light 

of the observation that some plant substances are initially feeding deterrents but 

lack toxicity if ingested. Azadirachtin is clearly an exception to this rule, as ingestion 

leads to deleterious physiological consequences, but many other compounds 

or extracts with demonstrated antifeedant effects lack toxicity when administered 

topically or via injection (8, 9). 

Repellents 

For many chemists, an effective alternative to DEET (N,N-diethyl-m-toluamide) 

for personal protection against mosquitoes and biting flies is the holy grail. In 

spite of five decades of research, no chemical has been found that provides the 

degree of protection against biting mosquitoes or persistence on human skin afforded 

by DEET (74). Concerns with the safety of DEET, especially to children, 

have resulted in the introduction of several plant oils as natural alternatives. Some 

personal repellents in the U.S. marketplace contain oils of citronella, eucalyptus, 

or cedarwood as active ingredients; 2-phenethylpropionate, a constituent of 

peanut oil, and p-menthane-3,8-diol (obtained from a particular species of mint) 

(Figure 2) are also used in consumer products. All of these materials can provide 

some protection, but the duration of their effect can be limited (often



CURRENT TRENDS IN THE USE OF BOTANICALS 

North America 

Europe 


At present, the United States allows the broadest range of botanical insecticides 

among industrialized countries, with registrations for pyrethrum, neem, rotenone, 

several essential oils, sabadilla, ryania, and nicotine (Table 1). Several azadirachtinbased 

(neem) insecticides are sold in the United States, and a number of plant 

essential oils are exempt from registration altogether. Canada has been more conservative 

with respect to pesticide registrations, allowing pyrethrum, rotenone, and 

nicotine, but only a handful of essential oils (73). Neem has yet to achieve full 

registration in Canada, to the disappointment of many organic growers. Mexico 

allows the use of most products sold in the United States, although there is no 

specific exemption for plant oils. 

Although considered by many in the agrochemical industry to be especially restrictive 

with respect to pesticide registrations, the European Union permits the use of 

pyrethrum, neem, rotenone, and nicotine, along with “components of etheric oils 

TABLE 1 Botanical insecticides approved for use in specific countries 

Country Pyrethrum Rotenone Nicotine Neem a Others 

Australia X X — — Citrus oils 

New Zealand X X — X 

India X X X X Ryania 

Philippines X — — — 

Hungary X — — — Quassia 

Denmark X X — — Lemongrass, clove, 

eucalyptus oils 

Germany X — — X 

Netherlands X — — — 

United Kingdom X X X — 

South Africa X — — — 

Brazil X X — X Garlic 

United States X X X X Specified essential oils, 

ryania, sabadilla 

Canada X X X — Specified essential oils 

Mexico X X — X Garlic, capsicum 

aIncludes insecticides listing azadirachtin as the active ingredient. 

Source: Reference 73 and personal communications (D. Badulescu, B. Chung, J. Immaraju & J. Vendramin).



58 ISMAN 

of plant origin” (73). Individual countries in western Europe show considerable 

variation in the botanicals they permit. For example, Hungary permits pyrethrum 

and nicotine, although the latter is severely restricted. Denmark permits only 

pyrethrum and rotenone, Germany pyrethrum and neem. The Netherlands permits 

pyrethrum alone. In spite of years of research on azadirachtin and neem in 

the United Kingdom, this botanical has never achieved registration there, leaving 

pyrethrum, rotenone, and nicotine as the only approved botanicals. 

Pacific/Asia 

India appears to embrace botanicals more than many other countries in the region, 

permitting all of the materials (save sabadilla) mentioned herein and allowing 

new products provisional registration while toxicological and environmental data 

in support of full registration are acquired. New Zealand has registrations for 

pyrethrum, rotenone, and neem, whereas Australia has yet to approve neem in 

spite of almost two decades of research and development in that country. Likewise, 

neem has yet to be approved for use in the Philippines, where pyrethrum is the 

only approved botanical insecticide. 

Latin America 

Africa 

In Brazil, each state has autonomous regulatory authority. Botanicals registered 

in most states include pyrethrum, rotenone, neem, and garlic, although nicotine 

and extracts of native plants are used to a small extent (J. Vendramin, personal 

communication). Throughout Latin America plant oils and extracts are produced 

by cottage industries on a small scale and used outside of any regulatory system 

on a regional basis (D. Badulescu, personal communication). 

Data on regulated insecticides are not readily available for most African countries. 

Among botanicals, only pyrethrum is approved for use in South Africa. As in 

Latin America, numerous crude plant extracts and oils are likely in local use in the 

poorer countries. 

Trends and Changes in Registration 

Given the ongoing negative perception of pesticides by the general public, government 

response to that perception, and increasing documentation of environmental 

contamination, it is hard to imagine pesticide regulators easing toxicological requirements 

for new pesticides, with the possible exception of certain plant oils 

and extracts widely used in human foods. Globalization of agricultural commodities 

will serve only to tighten restrictions on pesticide use in developing countries 

where fresh produce for export to wealthier countries is an important source of 

revenue. All produce imported into the European Union, United States, and Japan 

(for example) must comply with pesticide regulations in the respective importing




country, meeting the same standards as their own domestic produce. As a result, 

pesticide regulations set in the wealthiest countries have global reach—they affect 

growers directly in developing countries who are forced to comply. In short, a 

lack of confidence in the safety of a specific botanical insecticide by the European 

Union could make that product unfavorable in a tropical country, even where it 

makes sense for poorer growers providing agricultural produce for their domestic 

markets, and perhaps where the botanical source material grows and could be inexpensively 

prepared for crop protection. If nothing else, this review should highlight 

the fact that few new botanical insecticides are likely to see commercialization on 

a meaningful scale in the near future, in spite of the continual discovery of plant 

natural products with bioactivity against insect pests. 

DRAWBACKS AND BARRIERS TO COMMERCIALIZATION 

In reviewing this subject previously (44), I identified three main barriers to commercialization 

for botanical insecticides: sustainability of the botanical resource, 

standardization of chemically complex extracts, and regulatory approval. For each 

of these there are also important cost considerations. Other drawbacks or limitations 

are the slow action of many botanicals—growers must gain confidence in 

insecticides that do not produce an immediate “knockdown” effect—and the lack 

of residual action for most botanicals. 

Sustainability 

To produce a botanical insecticide on a commercial scale, the source plant biomass 

must be obtainable on an agricultural scale and preferably not on a seasonal 

basis. Unless the plant in question is extremely abundant in nature, or already 

grown for another purpose (e.g., sweetsop, Annona squamosa, grown for its 

edible fruit; rosemary, Rosmarinus officinale,asaflavoring), it must be amenable 

to cultivation. Pyrethrum and neem meet this criterion; the latter has been extensively 

introduced into Africa, Australia, and Latin America, more so as a shade 

tree, windbreak, or source of firewood than for its yield of natural medicines 

or insecticides. Research aimed at producing azadirachtin from neem tissue culture 

provided proof of concept, but economic feasibility has yet to be attained 

(2). 

In the not-too-distant future it may be possible to produce botanical insecticides 

by “phytopharming,” i.e., through genetic engineering of an existing field crop to 

produce high-value natural products originally isolated from a different botanical 

source. But as progress in plant biotechnology continues at a rapid pace, it may 

prove just as easy to modify the plants we wish to protect from pests directly, such 

that they produce the natural product protectant constitutively, alleviating the need 

to obtain the desired botanical product through extraction, formulate it, and then 

apply it to the crop we wish to protect. These sorts of technological advancements



60 ISMAN 

seem far more likely now than they did even a decade ago; however, the cost 

of these technologies will dictate that the traditional means of obtaining botanical 

insecticides, and indeed their minor uses (on small acreage specialty crops) or uses 

in developing countries on lesser value crops will continue for many years to come. 

Forexample, neem seed oil had a long history of use in India for the production of 

soaps and low grade industrial oil. When extraction companies began purchasing 

neem seeds in bulk to produce insecticides, the price of seeds increased 10-fold. 

In contrast, certain plant essential oils have numerous uses as fragrances and 

flavorings, and the massive volumes required to satisfy these industries maintain 

low prices that make their use as insecticides attractive. 

Standardization of Botanical Extracts 

An often cited drawback to the adoption of botanical insecticides by growers is the 

variation in performance of a particular product, even when prepared by the same 

process. Natural variation in the chemistry of a plant-based commodity should 

come as no surprise to anyone who enjoys coffee, tea, wine, or chocolate. Recent 

investigation of seed extracts from sweetsop (A. squamosa) collected in Indonesia 

demonstrated both geographical and annual variation in their insecticidal potency 

(60). For a botanical insecticide to provide a reliable level of efficacy to the user, 

there must be some degree of chemical standardization, presumably based on the 

putative active ingredient(s). This has certainly been achieved with more refined 

products based on pyrethrum, neem, and rotenone, but crude preparations often 

contain low concentrations of active ingredients without adequate quantitation. 

To achieve standardization, the producer must have an analytical method and the 

equipment necessary for analysis and may need to mix or blend extracts from 

different sources, which requires storage facilities and is partially dependent on 

the inherent stability of the active principles in the source plant material or extracts 

thereof held in storage (5). 

Regulatory Approval 

Regulatory approval remains the most formidable barrier to the commercialization 

of new botanical insecticides. In many jurisdictions, no distinction is made 

between synthetic pesticides and biopesticides, including botanicals. Simply put, 

the market for botanicals in industrialized countries—based mostly on uses in 

greenhouse production and organic agriculture—is too small to generate sufficient 

profits to offset multimillion dollar regulatory costs. Unfortunately, this situation 

may prevent many “green” pesticides from reaching the marketplace in 

countries where the demand is greatest. I am not making the case that botanicals 

should be exempt from all regulatory scrutiny; as discussed above, nicotine is 

as toxic and hazardous as many synthetic insecticides, and strychnine, still used 

for rodent and insect control in some regions, is responsible for some human 

poisonings (54). Natural products can pose risks, and safety cannot be assumed 

(25, 87). But most of the botanicals discussed in this review are characterized by




low mammalian toxicity, reduced effects on nontarget organisms, and minimal 

environmental persistence. 

As noted, several plant essential oils and their constituents are exempt from 

registration in the United States, attributed to their long use history as food and 

beverage flavorings or as culinary spices. This exemption has facilitated the rapid 

development and commercialization of insecticides based on these materials as 

active ingredients (46). Although other jurisdictions have yet to follow the lead 

of the United States in this regard, there are proposals in some Asian countries 

to exempt some types of pesticides from registration for specific uses in public 

health, for example, in head lice preparations or for cockroach and fly suppression. 

It seems that regulatory agencies continue to focus their efforts on protecting the 

general public from miniscule traces of pesticides in the food supply rather than 

focusing on the safety of applicators and farmworkers, for whom, arguably, the 

more demonstrable hazards occur. 

ROLE OF BOTANICALS IN THE FUTURE 

What role can botanical insecticides play in crop protection and for other uses in 

the near future? In industrialized countries it is hard to imagine botanicals playing 

a greater role than at present, except in organic food production. Organic production 

is estimated to be growing by 8% to 15% per annum in Europe and in North 

America (70), and it is in those marketplaces that botanicals face the fewest competitors. 

Even there, however, microbial insecticides and spinosad have proven 

efficacious and cost-effective. Rather than considered as stand-alone products, 

botanicals might be better placed as products in crop protectant rotations, especially 

in light of the documented resistance of the diamondback moth to Bacillus 

thuringiensis and spinosad due to overuse (85, 91). In conventional agriculture, 

botanicals face tremendous competition from the newest generation of “reduced 

risk” synthetic insecticides such as the neonicotinoids. Between 1998 and 2003, 

use of reduced risk pesticides in California increased more than threefold (from 

138 to 483 tons), whereas biopesticide use declined (from 652 to 472 tons) (18). 

Botanicals, constituting less than 1% of biopesticide use in California (18), are 

also in decline. Overall, it is hard not to conclude that the best role for botanicals 

in the wealthier countries is in public health (mosquito, cockroach abatement) and 

for consumer (home and garden) use. 

The real benefits of botanical insecticides can be best realized in developing 

countries, where farmers may not be able to afford synthetic insecticides and the 

traditional use of plants and plant derivatives for protection of stored products is 

long established. Even where synthetic insecticides are affordable to growers (e.g., 

through government subsidies), limited literacy and a lack of protective equipment 

result in thousands of accidental poisonings annually (35). 

Recent attention has been paid to traditional plants used in West Africa for 

postharvest protection against insects (6, 11, 12). Some of the more efficacious 

plants used have well-known active principles (e.g., rotenoids from Tephrosia,



62 ISMAN 

nicotine from Nicotiana, methyl salicylate from Securidaca, and eugenol from 

Ocimum); some of these are volatile and act as natural fumigants that kill adult 

pests and their progeny (52). At least one study indicates that these materials are 

relatively safe in the forms in which they are used (7). Some plant products could 

even be useful in industrialized countries for the protection of grain from storage 

pests (33). 

Many of the plants discussed in this review are tropical in distribution and theoretically 

available to growers in developing countries. However, efficacy against 

pests is only one factor in the adoption of botanicals—logistics of production, 

preparation, or use of botanicals can mitigate against their use (68). Perhaps it is 

time to refocus the attention of the research community toward the development 

and application of known botanicals rather than screen more plants and isolate 

further novel bioactive substances that satisfy our curiosity but are unlikely to be 

of much utility. 

ACKNOWLEDGMENTS 

I thank NSERC (Canada) and EcoSMART Technologies, Inc., for supporting original 

research on botanical insecticides and antifeedants in my laboratory. Industrial 

colleagues in western Europe, Latin America, and Australia provided information 

on registered botanical insecticides in their regions. 

The Annual Review of Entomology is online at http://ento.annualreviews.org 

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Annual Review of Entomology 

Volume 51, 2006 

CONTENTS 

SIGNALING AND FUNCTION OF INSULIN-LIKE PEPTIDES IN INSECTS, 

Qi Wu and Mark R. Brown 1 

PROSTAGLANDINS AND OTHER EICOSANOIDS IN INSECTS: BIOLOGICAL 

SIGNIFICANCE, David Stanley 25 

BOTANICAL INSECTICIDES,DETERRENTS, AND REPELLENTS IN 

MODERN AGRICULTURE AND AN INCREASINGLY REGULATED 

WORLD, Murray B. Isman 45 

INVASION BIOLOGY OF THRIPS, Joseph G. Morse and Mark S. Hoddle 67 

INSECT VECTORS OF PHYTOPLASMAS, Phyllis G. Weintraub 

and LeAnn Beanland 91 

INSECT ODOR AND TASTE RECEPTORS, Elissa A. Hallem, Anupama 

Dahanukar, and John R. Carlson 113 

INSECT BIODIVERSITY OF BOREAL PEAT BOGS, Karel Spitzer 

and Hugh V. Danks 137 

PLANT CHEMISTRY AND NATURAL ENEMY FITNESS: EFFECTS ON 

HERBIVORE AND NATURAL ENEMY INTERACTIONS, Paul J. Ode 163 

APPARENT COMPETITION,QUANTITATIVE FOOD WEBS, AND THE 

STRUCTURE OF PHYTOPHAGOUS INSECT COMMUNITIES, 

F.J. Frank van Veen, Rebecca J. Morris, and H. Charles J. Godfray 187 

STRUCTURE OF THE MUSHROOM BODIES OF THE INSECT BRAIN, 

Susan E. Fahrbach 209 

EVOLUTION OF DEVELOPMENTAL STRATEGIES IN PARASITIC 

HYMENOPTERA, Francesco Pennacchio and Michael R. Strand 233 

DOPA DECARBOXYLASE:AMODEL GENE-ENZYME SYSTEM FOR 

STUDYING DEVELOPMENT,BEHAVIOR, AND SYSTEMATICS, 

Ross B. Hodgetts and Sandra L. O’Keefe 259 

CONCEPTS AND APPLICATIONS OF TRAP CROPPING IN PEST 

MANAGEMENT, A.M. Shelton and F.R. Badenes-Perez 285 

HOST PLANT SELECTION BY APHIDS:BEHAVIORAL,EVOLUTIONARY, 

AND APPLIED PERSPECTIVES, Glen Powell, Colin R. Tosh, 

and Jim Hardie 309 

vii



viii CONTENTS 

BIZARRE INTERACTIONS AND ENDGAMES:ENTOMOPATHOGENIC 

FUNGI AND THEIR ARTHROPOD HOSTS, H.E. Roy, 

D.C. Steinkraus, J. Eilenberg, A.E. Hajek, and J.K. Pell 331 

CURRENT TRENDS IN QUARANTINE ENTOMOLOGY, Peter A. Follett 

and Lisa G. Neven 359 

THE ECOLOGICAL SIGNIFICANCE OF TALLGRASS PRAIRIE 

ARTHROPODS, Matt R. Whiles and Ralph E. Charlton 387 

MATING SYSTEMS OF BLOOD-FEEDING FLIES, Boaz Yuval 413 

CANNIBALISM, FOOD LIMITATION,INTRASPECIFIC COMPETITION, AND 

THE REGULATION OF SPIDER POPULATIONS, David H. Wise 441 

BIOGEOGRAPHIC AREAS AND TRANSITION ZONES OF LATIN AMERICA 

AND THE CARIBBEAN ISLANDS BASED ON PANBIOGEOGRAPHIC AND 

CLADISTIC ANALYSES OF THE ENTOMOFAUNA, Juan J. Morrone 467 

DEVELOPMENTS IN AQUATIC INSECT BIOMONITORING: A 

COMPARATIVE ANALYSIS OF RECENT APPROACHES, Núria Bonada, 

Narcís Prat, Vincent H. Resh, and Bernhard Statzner 495 

TACHINIDAE:EVOLUTION,BEHAVIOR, AND ECOLOGY, 

John O. Stireman, III, James E. O’Hara, and D. Monty Wood 525 

TICK PHEROMONES AND THEIR USE IN TICK CONTROL, 

Daniel E. Sonenshine 557 

CONFLICT RESOLUTION IN INSECT SOCIETIES, Francis L.W. Ratnieks, 

Kevin R. Foster, and Tom Wenseleers 581 

ASSESSING RISKS OF RELEASING EXOTIC BIOLOGICAL CONTROL 

AGENTS OF ARTHROPOD PESTS, J.C. van Lenteren, J. Bale, F. Bigler, 

H.M.T. Hokkanen, and A.J.M. Loomans 609 

DEFECATION BEHAVIOR AND ECOLOGY OF INSECTS, Martha R. Weiss 635 

PLANT-MEDIATED INTERACTIONS BETWEEN PATHOGENIC 

MICROORGANISMS AND HERBIVOROUS ARTHROPODS, 

Michael J. Stout, Jennifer S. Thaler, and Bart P.H.J. Thomma 663 

INDEXES 

Subject Index 691 

Cumulative Index of Contributing Authors, Volumes 42–51 717 

Cumulative Index of Chapter Titles, Volumes 42–51 722 

ERRATA 

An online log of corrections to Annual Review of Entomology 

chapters may be found at http://ento.annualreviews.org/errata.shtml

botanical insecticides, deterrents, and repellents in modern ...

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